We report on the transport study of a double quantum dot(DQD)device made from a freestanding,single crystalline InSb nanosheet.The freestanding nanosheet is grown by molecular beam epitaxy and the DQD is defined by the top gate technique.Through the transport measurements,we demonstrate how a single quantum dot(QD)and a DQD can be defined in an InSb nanosheet by tuning voltages applied to the top gates.We also measure the charge stability diagrams of the DQD and show that the charge states and the inter-dot coupling between the two individual QDs in the DQD can be efficiently regulated by the top gates.Numerical simulations for the potential profile and charge density distribution in the DQD have been performed and the results support the experimental findings and provide a better understanding of fabrication and transport characteristics of the DQD in the InSb nanosheet.The achieved DQD in the two-dimensional InSb nanosheet possesses pronounced benefits in lateral scaling and can thus serve as a new building block for the developments of quantum computation and quantum simulation technologies.
OBJECTIVE: To better understand the working mechanism of acupuncture, we investigated the skin electrical impedance distribution around acupoints, and the impedance changes at 12 original acupoints bilaterally after bending the limbs.METHODS: We measured the skin electrical impedance in three study subjects in the frequency range of 40 to 10 k Hz using the four-electrode method with a sharp probe and a large reference electrode.A measurement matrix of 7 mm × 7 mm with spacing of 2.0(or 3.0) mm was measured to obtain 2 D impedance mapping of acupoints. The impedance spectra of 12 original acupoints were measured at the 0° position and the 90° position.RESULTS: The electrical impedance of some acupoints, such as Yangchi(TE 4), was 16 times lower than that of the surrounding area, showing a recognizable small central area of low impedance with a diameter of less than 4 mm. In contrast, other acupoints, such as Laogong(PC 8), had an electrical impedance that was not significantly different from that of the surrounding area. When the limb was bent from a straight position(0o) to a vertical position(90o), the electrical impedance of the 12 original acupoints showed varied trends, either increasing or decreasing by a factor of up to ten times, or remaining at the same level.CONCLUSION: Not all acupoints tested show the property of low impedance, which might be related to the varied depth of the openings of superficial collaterals. The unexpected dependence of acupoint impedance on limb angle is a novel discovery, which implies that the channel paths are located in interstitial structures in the limbs. It might be possible to determine an optimized limb position for each particular acupuncture treatment in clinical practice.
An experimental realization of a ballistic superconductor proximitized semiconductor nanowire device is a necessary step towards engineering topological quantum electronics. Here, we report on ballistic transport in In Sb nanowires grown by molecular-beam epitaxy contacted by superconductor electrodes. At an elevated temperature, clear conductance plateaus are observed at zero magnetic field and in agreement with calculations based on the Landauer formula. At lower temperature, we have observed characteristic Fabry–Pérot patterns which confirm the ballistic nature of charge transport.Furthermore, the magnetoconductance measurements in the ballistic regime reveal a periodic variation related to the Fabry–Pérot oscillations. The result can be reasonably explained by taking into account the impact of magnetic field on the phase of ballistic electron＇s wave function, which is further verified by our simulation. Our results pave the way for better understanding of the quantum interference effects on the transport properties of In Sb nanowires in the ballistic regime as well as developing of novel device for topological quantum computations.
Sen LiGuang-Yao HuangJing-Kun GuoNing KangPhilippe CaroffHong-Qi Xu
We describe a simple method to increase the conductivity of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)(PEDOT:PSS)film by exposure to ultraviolet(UV)light in vacuum.Up to four order of conductivity improvement(from 10 3to 50 S/cm)is achieved by irradiating PEDOT:PSS film with 254 nm ultraviolet(UV)light.Increased conductivity in UV treated PEDOT:PSS film is stable under ambient exposure.The mechanism for conductivity improvement is investigated by current-voltage measurement,atomic force microscopy,and absorption spectrum.Photo-cross-linking of PSS chains is determined as the reason for conductivity improvement.Our result demonstrates that UV treatment is capable of modifying the conductivity of PEDOT:PSS film independent of the process of film formation.
An increase of work function （0.3 eV） is achieved by irradiating poly（3,4-ethylenedioxythiophene）：poly（styrene sul- fonate） （PEDOT：PSS） film in vacuum with 254-nm ultraviolet （UV） light. The mechanism for such an improvement is investigated by photoelectron yield spectroscopy, X-ray photo electron energy spectrum, and field emission technique. Sur- face oxidation and composition change are found as the reasons for work function increase. The UV-treated PEDOT：PSS film is used as the hole injection layer in a hole-only device. Hole injection is improved by UV-treated PEDOT：PSS film without baring the enlargement of film resistance. Our result demonstrates that UV treatment is more suitable for modifying the injection barrier than UV ozone exposure.
The hybrid graphene-quantum dot devices can potentially be used to tailor the electronic, optical, and chemical properties of graphene. Here, the low temperature electronic transport properties of bilayer graphene decorated with PbS colloid quantum dots(CQDs) have been investigated in the weak or strong magnetic fields. The presence of the CQDs introduces additional scattering potentials that alter the magnetotransport properties of the graphene layers, leading to the observation of a new set of magnetoconductance oscillations near zero magnetic field as well as the high-field quantum Hall regime.The results bring about a new strategy for exploring the quantum interference effects in two-dimensional materials which are sensitive to the surrounding electrostatic environment, and open up a new gateway for exploring the graphene sensing with quantum interference effects.
A gated Hall-bar device is made from an epitaxially grown,free-standing InSb nanosheet on a hexagonal boron nitride(hBN)dielectric/graphite gate structure and the electron transport properties in the InSb nanosheet are studied by gate-transfer characteristic and magnetotransport measurements at low temperatures.The measurements show that the carriers in the InSb nanosheet are of electrons and the carrier density in the nanosheet can be highly efficiently tuned by the graphite gate.The mobility of the electrons in the InSb nanosheet is extracted from low-field magneotransport measurements and a value of the mobility exceeding~1.8×10^(4) cm^(2)·V^(-1)·s^(-1) is found.High-field magentotransport measurements show well-defined Shubnikov-de Haas(SdH)oscillations in the longitudinal resistance of the InSb nanosheet.Temperature-dependent measurements of the SdH oscillations are carried out and key transport parameters,including the electron effective mass m*~0.028m0 and the quantum lifetimeτ~0.046 ps,in the InSb nanosheet are extracted.It is for the first time that such experimental measurements have been reported for a free-standing InSb nanosheet and the results obtained indicate that InSb nanosheet/hBN/graphite gate structures can be used to develop advanced quantum devices for novel physics studies and for quantum technology applications.
